The long-term goal of this proposed research is to identify the roles which different sensory inputs play and the operations performed by central neural structures in mediating some of the reflex behaviors which contribute to the control of vertical gaze and head posture. In particular, the research is directed toward the following objectives: (a) to characterize the interaction among vestibular, visual and neck proprioceptive inputs vis a vis the motor outputs, (b) to define the specific operations performed by the cerebellum and brain stem structures in mediating the reflex behaviors, and (c) to understand the pathophysiology underlying disorders of gaze and postural equilibrium and to identify adaptive strategies used by the central nervous system in compensating for vestibular deficits. The more specific aims of this proposal deal with the vertical semicircular canal and otolith interactions which are mediated by the interstitial nucleus of Cajal and other structures. Behaviorial observations and quantitative analyses of input-output relations will serve to define the dynamic characteristics of reflex responses. Single unit recordings in alert animals will indicate what information is transmitted over certain neural pathways and suggest the functions performed by specific neural structures. Mathematical modelling will provide a conceptual framework for identifying those essential features of the vertical vestibular and oculomotor systems which are invariant to the frame of reference used. Mathematical functions and geometrical representations will define these features. The experimental results of this work may well suggest protocols that could be used clinically to (1) test vertical canal and otolith organ function, (2) measure vestibulo-spinal reflexes, and (3) aid in differentiating between central and peripheral deficits in patients complaining of vertigo and dysequilibrium.